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Boat Safety Scheme - Fixed Ventilation

Is the vessel provided with adequate fixed ventilation?

Fixed ventilation is ventilation that cannot be closed without the use of tools.

Note - Ventilators, doors, windows, hatches and any other openings, which can be fully closed, must not be included in the ventilation calculation.

Note - Ventilators, doors, windows, hatches and any other openings, modified so they cannot be fully closed without the use of tools should only have their minimum fixed ventilation area included in the calculation.


The total effective area of fixed ventilation is: the total area of fixed ventilation provision, as measured.

Each ventilator, door, window, hatch and any other openings should be measured carefully to determine their individual effective area of fixed ventilation.

Careful examination must be made of each ventilator to determine the presence of any device which would reduce the clear air opening e.g.filter, insect screen, fan blades.

Where filters or screens are fitted, they must also be in a clean and serviceable condition as partial or complete blockage of the clear air openings could make the ventilator totally ineffective.

Louvered doors are a common form of providing fixed ventilation and the effective area needs to be carefully measured.

The total effective area of fixed ventilation is designed to provide:

  • combustion air for appliances that are not room‐sealed;
  • for the evacuation of combustion products from appliances that are not room sealed;
  • renewal of fresh air for habitation and comfort.


The formula used to calculate the fixed ventilation requirement (in mm2) is as follows:

  • = [2200 x U] + [650 x P] + [550 x H] + [440 x F], where:
  • U= input rating for all unflued appliances (inc. cookers) (in kW)
  • P = number of persons for which the accommodation space is designed
  • H = nominal output rating of all open‐flued solid fuel appliances (in kW)
  • F = input rating for all open‐flued appliances (in kW)
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